She was an art history major at Penn.

He was a student of business at Wharton.

One thing led to another, as it goes, and soon she gave him an old print of the university as a graduation gift.

Then she bestowed a colorful Miro print on paper.

And wouldn't you know? Next up was a print of Harvard, where he entered law school, as an engagement gift.

So it was that Katherine and Keith Sachs began acquiring art, back in the 1960s.

Needless to say, engagement led to a wedding. Art-buying, initially at a Newbury Street gallery in Boston and at Philadelphia's Mackler Gallery, transformed into real collecting. And now, after 45 years of marriage in May, the Sachses have decided to give 97 works of art, a substantial portion of their collection, to the Philadelphia Museum of Art.

To show its appreciation, the museum renamed its galleries of modern and contemporary art the Keith L. and Katherine Sachs Galleries at a dedication ceremony Monday evening.

In summer 2016, the museum will present a full-scale show devoted to the Sachs collection, accompanied by a scholarly catalog, in the Dorrance Special Exhibition Galleries.

The gift, focusing almost exclusively on art made after World War II, instantly transports the museum into the front ranks of major encyclopedic museums with contemporary work.

When the gift was announced in January, Timothy Rub, museum director, hailed the collection as "a wonderful game-changer for us."

Jasper Johns, Ellsworth Kelly, Richard Serra, Brice Marden, Joseph Beuys, Richard Hamilton, Howard Hodgkin, Scott Burton, John Chamberlain, Tony Smith, Steve McQueen, Donald Judd, Anselm Kiefer, Joel Shapiro, Kiki Smith, Neil Jenney - the list of modern and contemporary masters collected by the Sachses rolls on and on.

"When we started collecting, we never intended to do anything other than gift it," Keith Sachs said recently, as the couple chatted about art, artists, collecting, relationships, the museum, the university, and a host of other topics. "Never expected to buy it and sell it or give it to the kids. . . . We live here, we grew up here in terms of the museum world, and this is where we've tried to have an impact on the community and the art world."

Keith Sachs, 68, is direct and analytical in conversation. He is the former head of a firm that supplies packaging to wine and spirits businesses and has been a trustee of the museum since 1988.

Katherine Sachs, 66, friendly and deeply informed about art, practically moved directly into the museum when she graduated from Penn in 1969. She worked in the public relations department and then served as a volunteer in several capacities. She has put her expertise to use as an exhibition scholar, working with the museum's department of European art before 1900, and she was a cocurator of the museum's 2009 exhibition "Cézanne and Beyond."

"What's interesting is when you change from buying to collecting," she said, thinking about the acquisition of art. "I think the key factor, at least for me, is being involved in the museum so early. You had a certain sense of what was really good, and the more we learned, the more we realized maybe the things we first bought weren't so good. But we really like living with good things. So you move in that direction."

They were buying Hans Hofmann, Franz Kline, and other abstract expressionist artists, but the work was difficult to get and often too expensive.

"So we had to think about what it is that would be interesting for us that we could afford," Keith Sachs said. "We started to look at people more of our generation than of the [abstract expressionist] generation."

Mark Rosenthal, the art museum's former curator of contemporary art, was extremely helpful in focusing their attention. Rosenthal backed their interest in Jenney, Kiefer, Marden - all acquired by the Saches and promised now to the museum.

"We weren't pop-oriented - we liked more abstract works of art," said Kathy Sachs. "I think it was just this more abstract, emotional kind of art, something that clicked, and I think once there was enough of it we realized, let's not venture too far off one way or the other."

They date their "collecting" to the early to mid-1980s.

"We decided, 'OK, these are the people we want to buy,' " she continued. "We had hit lists of people that we wanted to have and it took years for us to get through the lists. It really did. It was exciting. It structured you in a certain way, but it was very important."

An early milestone was a work the Sachses commissioned from sculptor Richard Serra.

"There were painters we wanted to go after; Richard we also wanted to go after," said Keith Sachs. "That piece we got in 1988. We started the process in 1985, it just took a while to find the right person to help us make it all happen. That was an instance of we wanted to get it and we were happy to offer whatever part of our house Richard wanted to take over to create the commission."

The result is Serra's Equal Elevations On and In to Kathy and Keith, two parallel Corten steel walls, 10½ feet high by 20 feet long, slightly tilted. Both Saches believe the work has great, dislocating power.

"How an artist, with very cold material, no color, can still make you feel as strongly as you do" is what Kathy Sachs finds astonishing, she said.

"How he can change your sense of the world, your sense of balance, your sense of reality because of what he does," she said, ticking off multiple appeals. "The way of the work, the tension of the work, the sense of foreboding - [the walls] could just fall! - but how he can change the atmosphere around you is what is amazing about Richard. In our piece, it's how he could make alive empty space, which is really what is between the two walls out there. He can energize that."

Kelly, Hodgkin, and other abstract and minimalist artists share a similar ability to ignite emotion, said Keith Sachs. Their power is sophisticated and raw at the same time.

"In my business life, I'm dealing with people who have certain things on their minds, and the opportunity to meet with and discuss things with these artists, which was entirely different than the conversations that I had in my business life, was tremendous," said Keith Sachs.

"I used to say to Kathy when we had people for dinner, 'This is unbelievable. This is not the kind of conversation that we'd have at a business dinner.' . . . It's for me so personally refreshing to see these different viewpoints."